The effects of the grain boundary modifiers H3BO3, and SiO2 before and after the calcination steps on the microstructure and on the positive temperature coefficient of resistivity (PTCR) of Sb2O3 donor doped Ti-excess barium titanate (BT) were investigated. The additions before calcination resulted in coarse porosity between the grains and the additions after calcination gave rounded, uniform grains with a pronounced decrease in porosity. The Sb2O3 donor-doped BT became conductive when sintered at 1300 degrees C giving a room temperature resistivity (rho(RT)) of 400 OhM cm. The rho(RT) values of the B2O3 and SiO2 contained samples decreased when modifiers were added after the calcination step. The Sb2O3 donor-doped BT showed a PTCR effect of 4.2 orders of magnitude and a range of 4.5-5.0 orders of magnitude were obtained for the B2O3 and SiO2 added samples.